1. Field of the Invention
The present invention generally relates to variable valve actuation devices for use with internal combustion engines. More specifically, this invention relates to a novel architecture for a lifter plate arrangement used in varying valve timing of an overhead camshaft engine.
2. Description of the Prior Art
Conventionally, valve trains of internal combustion engines include poppet valves that are spring loaded toward a valve-closed position. The poppet valves are biased open by a lifter plate or tappet interposed each poppet valve and an overhead camshaft mechanism, or a camshaft and push rod mechanism. In either case, the camshaft is connected to and rotates in synchronization with an engine crankshaft to open and close each valve at predetermined intervals as defined by the position of lobes on the camshaft. Therefore, the sequence and lift distance of each valve is fixed by the predetermined relationship between the lifter plate and the lobes on the camshaft.
Such direct-drive arrangements fix valve train operation and thereby limit engine performance because ideal valve timing variesxe2x80x94and is not fixedxe2x80x94over the full range of engine speed. Therefore, it would be desirable to incorporate a variable drive arrangement in which the valve train is not fixed, but is independently variable with respect to each valve. In other words, valve lift distance and timing could be varied independently for each valve. These factors can be varied to improve breathing of the engine to increase performance, fuel economy, or emissions.
Consequently, what is needed is a variable valve actuation system that packages tightly within an engine and permits independent variability of the timing of each valve.
According to the present invention, there is provided a variable valve actuation (VVA) system. The VVA system is used in conjunction with an overhead camshaft that has a series of camshaft lobes thereon. An engine valve terminates in a stem end and is moveable between open and closed positions along its own longitudinal axis, where the valve is biased toward the closed position. A bucket tappet includes a lifter plate that has a middle portion for engaging the lobe of the camshaft on a lobe side of the lifter plate and for engaging the stem end of the valve on a valve side of the lifter plate. The lifter plate includes end portions on either side of the middle portion, and is translatable by rotation of the lobe of the camshaft to cause movement of the valve along its longitudinal axis toward the open position. Finally, a pivoting device is in engagement with at least one of the end portions of the lifter plate, for pivoting the lifter plate toward the lobe for early engagement therewith and for pivoting the lifter plate away from the lobe for delayed engagement therewith. The early engagement causes the valve to open prematurely and the delayed engagement causes the valve to open belatedly.
Accordingly, it is an object of the present invention to provide a VVA system that is capable of both varying the timing of the valve opening and closing, and varying the duration of the opening of the valve.
It is another object of the present invention to provide a VVA system that packages tightly, if not symmetrically, around a valve stem of a valve.
It is yet another object to provide a VVA system that incorporates a bucket tappet having a variable angle lifter plate disposed between a camshaft lobe and a valve.
These objects and other features, aspects, and advantages of this invention will be more apparent after a reading of the following detailed description, appended claims, and accompanying drawings.